PNaCl: Add option to PNaClABISimplify for enabling the PNaClSjLjEH pass

Making this an 'enable' option (rather than using the pass name,
"-pnacl-sjlj-eh") will allow us to reorder the passes within
PNaClABISimplify.cpp later without having to change pnacl-ld.py (which
lives outside the pnacl-llvm repo).

It also means that the option can turn off LowerInvoke, which might
reduce the link time a little.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3696
TEST=tested with PNaCl-side plumbing in pnacl-ld.py etc.

Review URL: https://codereview.chromium.org/33743010

1 files changed, 20 insertions, 5 deletions

diff --git a/lib/Transforms/NaCl/PNaClABISimplify.cpp b/lib/Transforms/NaCl/PNaClABISimplify.cpp
index 5d64b088ce..d695f61203 100644
--- a/lib/Transforms/NaCl/PNaClABISimplify.cpp
+++ b/lib/Transforms/NaCl/PNaClABISimplify.cpp
@@ -21,7 +21,27 @@
 
 using namespace llvm;
 
+static cl::opt<bool>
+EnableSjLjEH("enable-pnacl-sjlj-eh",
+             cl::desc("Enable use of SJLJ-based C++ exception handling "
+                      "as part of the pnacl-abi-simplify passes"),
+             cl::init(false));
+
 void llvm::PNaClABISimplifyAddPreOptPasses(PassManager &PM) {
+  if (EnableSjLjEH) {
+    // This comes before ExpandTls because it introduces references to
+    // a TLS variable, __pnacl_eh_stack.  This comes before
+    // InternalizePass because it assumes various variables (including
+    // __pnacl_eh_stack) have not been internalized yet.
+    PM.add(createPNaClSjLjEHPass());
+  } else {
+    // LowerInvoke prevents use of C++ exception handling by removing
+    // references to BasicBlocks which handle exceptions.
+    PM.add(createLowerInvokePass());
+    // Remove landingpad blocks made unreachable by LowerInvoke.
+    PM.add(createCFGSimplificationPass());
+  }
+
   // Internalize all symbols in the module except _start, which is the only
   // symbol a stable PNaCl pexe is allowed to export.
   const char *SymbolsToPreserve[] = { "_start" };
@@ -32,11 +52,6 @@ void llvm::PNaClABISimplifyAddPreOptPasses(PassManager &PM) {
   PM.add(createLowerExpectIntrinsicPass());
   // Rewrite unsupported intrinsics to simpler and portable constructs.
   PM.add(createRewriteLLVMIntrinsicsPass());
-  // LowerInvoke prevents use of C++ exception handling, which is not
-  // yet supported in the PNaCl ABI.
-  PM.add(createLowerInvokePass());
-  // Remove landingpad blocks made unreachable by LowerInvoke.
-  PM.add(createCFGSimplificationPass());
 
   // Expand out some uses of struct types.
   PM.add(createExpandArithWithOverflowPass());